This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application PAD STRUCTURE OF SEMICONDUCTOR PACKAGE filed with the Korean Industrial Property Office on Jul. 20, 1999 and there duly assigned Serial No. 29391/1999.
1. Field of the Invention
The present invention relates to semiconductor packages, specifically to semiconductor packages with pad structures formed on Printed Circuit Boards (PCBs) improved to prevent short circuits.
2. Description of the Prior Art
Generally, a semiconductor package comprises a semiconductor body and a plurality of leads extending from the semiconductor. Such semiconductor packages are secured to a PCB by such methods as soldering.
Recently, as the number of leads extending from the semiconductor has increased due to a high degree of integration, the spacing between the leads has tended to become shorter. As the spacing between the leads decreases, short circuits caused by contacts between the leads occur more frequently. Therefore, it is necessary to secure a plurality of leads with small spacing onto the PCB effectively.
A typical semiconductor package comprises a semiconductor body and a plurality of leads extending from both sides of the semiconductor body. On the PCB at locations corresponding to the leads, a plurality of pads are formed. At the middle portion of the pad, a squared pad portion is formed. When securing the package onto the PCB, the leads are soldered to the engaging portions and the squared pad portions.
However, when the lead is attached to the pad, the squared portions of the pad protrude laterally, forming a contact portion abutting with the squared portion of the adjacent pad. This causes short circuits which deteriorate the performance of the semiconductor.
Generally, flatness of the pad is maintained within 80 to 100 xcexcm. The lead is attached to the pad uniformly when such flatness is maintained. However, when the end portions of the connectors and leads of a quad flat pack (QFP) are raised upward to a predetermined height rendering the flatness in excess of 150 xcexcm, the lead may float or the leads may not be attached to the pad properly. This may also cause inadequate tensile strength.
Furthermore, since the squared pad portion is formed at the middle portion of the pad, the lead tends to be fused only to both lateral sides of the middle portions of the lead. Therefore, when the lead is not maintained horizontal to a predetermined degree, the forward or rear portion tends to float with only the middle portion being attached, reducing the tensile strength.
It is therefore an object of the present invention to provide an improved pad structure for a semiconductor package.
It is a further object of the invention to provide a pad structure which is resistant to the formation of short circuits between the leads during soldering.
It is a yet further object of the invention to provide a pad structure which has an increased tensile strength.
It is a still further object of the invention to provide a pad structure which prevents floating of the leads even if the leads are perfectly flat.
The above and other objects, advantages and features of the present invention will become more readily appreciated and understood from a consideration of the following detailed description of a preferred embodiment of this invention when taken together with the accompanying drawings.
In order to achieve the above objects, a pad structure for a semiconductor package according to the present invention comprises: a printed circuit board with solder lands formed on predetermined portions thereof; and a plurality of pads formed on upper surfaces of the solder lands to which a plurality of leads of the semiconductor package is attached, first circular pad portions protruding laterally from lateral sides of the pads, second circular pad portions protruding laterally from other lateral sides of the pads, wherein the leads are secured to the pads of the semiconductor package so that when the first and second circular pad portions are pushed laterally, the circular pad portions do not contact each other which prevents short circuits.
Preferably, heights of the first and the second circular pad portions are identical to heights of the pads, the first and second circular pad portions protruding upward to a predetermined height due to surface tension, raising the height of the pad when the leads are secured to the pads, the leads depressed for a predetermined depth and then bonded so that the leads are secured to the pads even when the leads are not horizontal.
More preferably, the first and second circular pads are fused to both lateral sides of the leads, resisting force exerted in lateral directions when the leads are secured to the pads.
In order to achieve the above objects, a pad structure for a semiconductor package according to the present invention may comprise: a printed circuit board with solder lands formed on predetermined portions thereof; and a plurality of pads formed on upper surfaces of the solder lands, first pads with circular pad portions formed on predetermined locations thereof, second pads with circular pad portions disposed in alternating manner with respect to the circular pad portions of the first pads formed on predetermined locations thereof, the first pads and the second pads continuously repeated on the pads, wherein the leads are secured to the pads so that when the first and second circular pad portions are pushed laterally, the circular pad portions do not contact each other whereby short circuits are prevented.
Preferably, heights of the first and the second circular pad portions are identical to heights of the pads, the first and second circular pad portions protruding upward to a predetermined height due to surface tension raising the height of the pad when the leads are secured to the pads, the leads depressed for a predetermined depth and then bonded so that the leads are secured to the pads even when the leads are not horizontal.
More preferably, the first and second circular pads are fused to both lateral sides of the leads, resisting force exerted in lateral direction when the leads are secured to the pads.